In the latest example of a health-tech startup battling regulators, Opternative, the startup that lets you get a prescription without visiting an eye doctor, is suing South Carolina for the right to operate there.

Since the Chicago startup launched last year, allowing customers to self-perform a $40 vision test on its website and receive a corrective-lens prescription, it's come under fire by optometrists who call the service unproven and potentially unsafe. The American Optometric Association and local optometrist groups have lobbied against it, including in South Carolina, where a recently passed law prohibits Opternative's business model. Similar bans are also on the books in Georgia and Indiana; otherwise, Opternative operates in 39 states.

When customers take a test on Opternative, an ophthalmologist licensed in their state reviews their results. But South Carolina's Eye Care Consumer Protection Law, passed in May, mandates that vision tests "may not be based solely on objective refractive data or information generated by an automated testing device, including an auto refractor or other electronic refractive-only testing device, to provide a medical diagnosis or to establish a refractive error for a patient as part of an eye examination."

So on Thursday, with the help of the libertarian law firm Institute for Justice, Opternative filed a lawsuit against the state of South Carolina in civil court. The company argues that the law violates the state's constitution because it deprives Opternative "of its constitutional right to pursue an honest living," and solely exists to reduce "access to online eye care in South Carolina in order to prop up professional optometrists' outdated business model."

"They have not passed a law to protect people from any actual threat to public health or safety," Robert McNamara, a senior attorney at the Institute for Justice, told BuzzFeed News.

The lawsuit notes that Gov. Nikki Haley vetoed the law, and said that "it uses health practice mandates to stifle competition for the benefit of a single industry," but the legislature overrode her. Opternative also says that South Carolina lawmakers passed a separate law this year that allows telemedicine services in general to operate — but explicitly prohibits ophthalmologists from writing prescriptions for online services such as Opternative.

Optometrists who oppose Opternative say that because it does not offer a comprehensive eye health exam — which the site acknowledges on its website — customers potentially miss out on meeting in person with a professional who could catch eye diseases and other problems.

Optometrists also say there is little to no proof that the service can deliver accurate corrective-lens prescriptions as advertised. As evidence of its efficacy, Opternative cites an independently run study that involved 30 people. It has not been published in a peer-reviewed scientific journal.

Asked if Opternative planned to also sue in Georgia and Indiana, CEO Aaron Dallek said in a statement, "I never make threats about lawsuits, and I have every hope that we can find ways to work productively and legally in all 50 states without litigation. But we absolutely believe in our constitutional right to earn a living free from arbitrary government interference, and we're happy to defend that right like we are in South Carolina."

In a statement, Barbara Horn, the American Optometric Association's secretary-treasurer and an optometrist in Conway, South Carolina, slammed Opternative and the Institute for Justice. “Having lost decisively in our state capital and still lacking any credible research or federal medical device approvals, they’ve come back to try to impose their profit-driven approach to health care on South Carolina," she said on behalf of the association. "Their questionable legal tactics will cost the citizens of our state time and money — resources better invested in protecting the health of our patients. South Carolinians deserve better, and my fellow doctors and I, patients and public health experts across the state will continue to speak out and expose their schemes.”

UPDATE

Oct. 20, 2016, at 21:22 PM

This story has been updated to include a comment from the American Optometric Association.

Stephanie M. Lee is a science reporter for BuzzFeed News and is based in San Francisco.